The invention relates to a method for operating a closed hot-water installation provided with a pipe system having a boiler and at least one heat exchanger and an expansion tank, a water make-up provision and a de-aerator, disposed at the highest point of the installation and comprising a non-return valve which is mounted in an air head and opens at a predetermined pressure to allow air to escape from the closed installation, the water level in the de-aerator being detected for feeding water to the closed installation via the water make-up provision when the level becomes too low. The invention also relates to an apparatus to be used with such method.
Such method and apparatus are known from Dutch patent specification 1000494, wherein the non-return valve determines the maximal working pressure, because de-aeration takes place at that maximal working pressure. If one wishes to be able to have that working pressure vary between reasonable limits, this can be regarded as a limiting factor for de-aeration.
The object of the invention is to provide more flexibility for the system, more in particular to provide a possibility for de-aerating below the maximal working pressure.
In accordance with the invention, in a method of the type mentioned in the preamble, this object is realized when the opening of the non-return valve is blocked until it is detected that the water level has fallen to a first level and the feed of water is started when a second, lower level is reached. Due to these features, the non-return valve can be set at any desired pressure, for instance the minimally required working pressure, which promotes the de-aerating possibilities. Indeed, through the level-dependent blocking of the non-return valve, the non-return valve is blocked against blowing off in the case of an insufficiently great air head. This implies that independently of the blow-off pressure of the non-return valve, such a great air head is in each case present that it is guaranteed that the water level cannot rise so high that dirt floating on that water can reach the non-return valve and the make-up valve, which could disturb the proper operation of those valves due to fouling. The blocking of the non-return valve also prevents the situation that in the event of a failure in the make-up valve, water can leak away via the non-return valve. In this manner, a failure-free, optimal de-aeration can advantageously be achieved at a working pressure varying within usual limits.
The blocking of the non-return valve can be realized relatively easily if, in accordance with a further embodiment of the invention, the detection of the first and the second water level is carried out by means of a float. This manner of operating can be optimized still further if the detection of the first and the second water level is carried out by means of one single float, whereby, when the first level is reached, a blocking of the de-aerator is removed and, when the second level is reached, the water make-up provision is opened.
The invention also relates to an apparatus which can be used with a method according to the invention as discussed hereinabove. To that end, an apparatus for discharging air from and feeding water to a closed hot-water installation is provided with a pipe system having a boiler and at least one heat exchanger, which apparatus, as known from Dutch patent specification 1000494, comprises a housing having a bottom side that can be brought into open communication with the pipe system and comprising, adjacent its top side, a vent valve and a water make-up valve which can be opened by a float displaceable in the housing. In accordance with the invention, the vent valve comprises a blocking member which in a blocking position shuts off the access to the vent valve and which can be moved into and out of said blocking position by a float displaceable in the housing. More in particular, it is preferred that the make-up valve and the blocking member be operated by one and the same float, while starting from the make-up valve in the open position and the blocking member in the position in which the access to the vent valve is released, the float, during a displacement in the direction of the make-up valve and the blocking member, shuts off the make-up valve first and, after a continued displacement, moves the blocking member into its blocking position. In this manner, the blocking of the non-return valve can be realized by extremely simple and minimal means.
In this manner, in accordance with the invention, a vent valve can be used in the form of a non-return valve which prevents connection with the environment during float-controlled opening of the de-aerating means and at a pressure in the housing lower than the ambient pressure. In other words: a non-return valve with a blow-off pressure which can be equal to the minimal working pressure. If so desired, that non-return valve may also be adjusted to any other pressure between the minimal and the maximal working pressure, because the blocking member closes off the access to the non-return valve if the air head has been reduced to a fixed value.
The blocking member and the non-return valve can be designed in many manners. A number of preferred embodiments are described in the claims and will be specified hereinafter.